This crushing process is generally a first step in the recovery process of fats and other by-products form offal and use is thereby made of conventional offal crushers comprising a comminuting chamber in which a rotatable shaft is arranged bearing a set of side by side arranged knifes which pass through calibrated slots between stationary elements thereby shredding the raw material fed into the chamber. Up to now the knifes were arranged on said shaft so that an imaginary line connecting the consecutive knife-tops from one end of the shaft towards the other is a helicoid or almost a helicoid. A disadvantage of this kind of arrangement of the knives relates to the relatively high energy consumption for a certain output of the crusher. This is mainly due to the fact that the consecutive cutting positions of the knifes regularly shift from one end of the crusher to the other. Each next cutting position is thus very close to the previous one and so each next knife generally hinders a deep penetration of the previous knife top in the material to be crushed. This has as a consequence that the knives on each cutting action only tear relatively small pieces away of the material and that the material (certainly when it is in the form of pieces or lumps with large volumes) continues to tumble on top of the knife cams and thereby builds a sort of a bridge above the rotating knives between the side walls of the chamber. This decreases the output of the crusher.